# How to copy a lemma to appendix without changing its number?

I have a document with a lemma (using amsthm), like so:

\begin{lem} \label{mylemma}
% ...
\end{lem}

The proof of this lemma can be found in the appendix (see section \ref{sec:proof_of_mylemma}).


I now place a copy of the lemma in the appendix, with proof included:

\section{Appendix}

\section{Proof of lemma \ref{mylemma}} \label{sec:proof_of_my_lemma}

\begin{lem}
% ...
\end{lem}

\begin{proof}
% ...
\end{proof}


The problem is that the second copy of my lemma has a new number. How can I renumber this lemma to mimick the number of mylemma?

Thanks!

-
– barbara beeton Feb 4 '14 at 13:31

You can use the restatable environment provided by the thmtools package:

\documentclass{article}
\usepackage{amsthm}
\usepackage{thmtools,thm-restate}

\newtheorem{lem}{Lemma}

\begin{document}

\begin{restatable}{lem}{primelemma}
\label{mylemma}
Let $p$ be a prime number, and assume $p$ divides the product of two integers $a$ and $b$. Then $p$ divides $a$ or $p$ divides $b$.
\end{restatable}

\section{Proof of lemma~\ref{mylemma}}
\primelemma*

\end{document}


-
What about the opposite: cite the lemma before? For example, cite on Introduction the Lema 1.2 with the same numbering. – Sigur Feb 4 '14 at 14:03
@Sigur in that case, use the starred version restatable* in the Introduction and the un-starred \primelemma further on in the document. – Gonzalo Medina Feb 4 '14 at 16:57